This invention relates to an energy recovery device particularly but not exclusively for use in combination with reverse osmosis equipment such as is used, for example, in the desalination of water.
Desalination plants are required to operate at the highest possible efficiency in order to keep the cost of water to a minimum. It is well known to employ energy recovery devices to recover energy from the waste liquor of reverse osmosis equipment. There are various known devices for recovering energy by changing the pressure energy of the waste liquor to shaft work, such as turbines, Pelton wheels and reverse running pumps. However, the conversion of fluid pressure to shaft work and then back again to fluid pressure is inherently less efficient than using fluid pressure directly.
It is also known, such as from U.S. Pat. No. 5,306,428, to use work exchangers to transfer the fluid pressure of the waste liquor across a piston. However, there is a pressure drop across the reverse osmosis equipment and known recovery systems employing a piston to transfer the pressure of the waste liquor to feed liquid require the use of a booster pump to raise the pressure of the liquid exiting from the work exchanger to the inlet pressure of the reverse osmosis equipment.
According to a first aspect of the present invention there is provided an energy recovery device comprising at least one cylinder, a piston slidable in the cylinder, first valve means for selectively connecting one end of the cylinder to waste liquid at a first relatively high pressure and to drain, second valve means for allowing feed liquid to enter the other end of the cylinder at a second lower pressure via a feed liquid entry port and to be discharged via a feed liquid discharge port from the other end of the cylinder in response to movement of the piston caused by waste liquid entering said one end of the cylinder, and means ensuring that the area of the piston acting, in use, on the feed liquid is less than the area of the piston, in use, acted upon by the waste liquid so that the piston acts as a pressure intensifier to discharge feed liquid through the feed liquid discharge port at a higher pressure than the pressure of waste liquid entering said one end of the cylinder.
According to a second aspect of the invention, there is provided an energy recovery device comprising a valve housing, a slidable valve element in the valve housing and two cylinders extending from the valve housing in a direction transverse to the axis of movement of the valve element, the slidable valve element controlling the flow of liquid to and from both cylinders.
According to a third aspect of the invention there is provided an energy recovery device according to the first or the second aspect of the invention in combination with reverse osmosis equipment.
The invention will now be more particularly described, by way of example, with reference to the accompanying drawings.